The present invention relates to ink jet printing on a receiver that is rotated by a drum.
Ink jet printing has become a prominent contender in the digital output arena because of its non-impact, low-noise characteristics, and its compatibility with plain paper. Inkjet printers avoid the complications of toner transfers and fixing as in electrophotography, and the pressure contact at the printing interface as in thermal resistive printing technologies. Ink jet printing mechanisms includes continuous ink jet or drop-on-demand ink jet. U.S. Pat. No. 3,946,398, which issued to Kyser et al. in 1970, discloses a drop-on-demand ink jet printer which applies a high voltage to a piezoelectric crystal, causing the crystal to bend, applying pressure on an ink reservoir and jetting drops on demand. Piezoelectric ink jet printers can also utilize piezoelectric crystals in push mode, shear mode, and squeeze mode. EP 827 833 A2 and WO 98/08687 disclose a piezoelectric ink jet print head apparatus with reduced crosstalk between channels, improved ink protection, and capability of ejecting variable ink drop size.
U.S. Pat. No. 4,723,129, which issued to Endo et al. in 1979, discloses an electrothermal drop-on-demand ink jet printer which applies a power pulse to an electrothermal heater which is in thermal contact with water based ink in a nozzle. A small quantity of ink rapidly evaporates, forming a bubble which causes an ink drop to be ejected from small apertures along the edge of the heater substrate. This technology is known as Bubblejet(trademark) (trademark of Canon K. K. of Japan).
U.S. Pat. No. 4,490,728, which issued to Vaught et al. in 1982, discloses an electrothermal drop ejection system which also operates by bubble formation to eject drops in a direction normal to the plane of the heater substrate. As used herein, the term xe2x80x9cthermal ink jetxe2x80x9d is used to refer to both this system and system commonly known as Bubblejet(trademark).
Drum based receiver transport mechanism has the advantages of small foot print and the capabilities of uni-directional printing with high printing duty cycles. The printing of an image can be made by an index mode in which the print head translates to a position and stays there while printing a swath of image while the drum rotates along the fast-scan direction. After the swath is finished, the print head is translated again to the next printing position, the next swath is printed. This printing method requires the print head to move between printing swaths, which is a non-printing overhead to the operation and thus lowers throughput.
The ink image can also be printed on the drum surface by simultaneously translating the print head and rotating the drum. The ink nozzles produce spiral or helical paths on the ink receiver attached to the drum surface. One difficulty of this technique is that the helical paths produce a skew between the columns and rows of ink dots, as described in U.S. Pat. Nos. 4,112,469 and 4,131,898. The skew increases with the print head width. The skew becomes very severe for wide print heads (1xe2x80x3, 2xe2x80x3 to page wide).
U.S. Pat. No. 5,889,534 discloses calibration and registration method for manufacturing a drum based printing system. The receiver is skewed to produce a square image comer. This technique, however, requires the receiver to be precisely skewed relative to the drum axis, which is often difficult. In addition, the timing of the ink drop ejection needs to be precisely varied between nozzles to provide tilted rows of ink dots (FIG. 19).
An object of the present invention is to provide quality ink images on a receiver attached to a rotating drum.
This object is achieved by ink jet printing apparatus in response to a digital image for forming an ink image on a receiver attached to the surface of a drum rotatable about an axis, comprising:
a) an actuable ink jet print head movable in a direction parallel to he drum axis for delivering ink to the receiver;
b) means for rotating the drum such that the attached receiver moves at a predetermined surface velocity;
c) means for moving the ink jet print head at a velocity less than the predetermined velocity of the receiver so that the print head scans an area of drum surface that is skewed relative to the drum axis; and
d) control means responsive to the digital image for simultaneously controlling the rotating and the moving means and means for actuating the ink jet print head to form an ink image within the scanned area wherein two edges of the ink image are parallel to the drum axis and two edges of the ink image are perpendicular to the drum axis.
A feature of the present invention is to provide images with two edges being perpendicular the drum axis and two edges being parallel to the drum axis.
One advantage of the present invention is that the ink receiver can be easily aligned on the drum surface.
Another advantage of the present invention is that the ink nozzles in an ink jet print head can be aligned along the drum axis to permit simultaneous ejection of ink drops from different ink nozzles.